The present invention relates to a method for fabricating a semiconductor structure, and in particular to a method for reducing damage to a semiconductor structure resulting from migration of constituents of a first component part of the structure into a subsequently deposited second component part of the structure which makes contact with the surface of the first component part.
It is well known that if a material such as pure aluminium is deposited on for example a silicon substrate constituents of the silicon substrate migrate into the pure aluminium and vice versa. If the contact area between the aluminium and the silicon is relatively large and the deposited aluminium is relatively thin, the migration of silicon material into the aluminium does not result in substantial damage to the silicon surface. If however the contact area is relatively small as compared with the volume of the aluminium substantial damage can be caused to the silicon surface. This can occur where for example aluminium is used to make contact with a silicon surface through a hole formed in an insulating layer formed over the silicon surface. The problem has become more severe as the minimum size of individual semiconductor structure features has reduced, for example the minimum size of a through hole formed in an insulating layer.
It is known to address this problem by pre-doping a material such as aluminium before it is deposited. Unfortunately the use of pre-doped aluminium is less advantageous as compared with the used of pure aluminium with the exception of the damage that can result to an underlying silicon surface of relatively small area.
It is an object of the present invention to obviate or mitigate the problems outlined above.
According to the present invention, there is provided a method for reducing damage to a semiconductor structure resulting from migration of constituents of a first component part of the structure into a subsequently deposited second component part of the structure which makes contact with a surface of the first component part, wherein a third component part of the structure is deposited before the second component part, the third component part being positioned to be contacted by the second component part adjacent the said surface, and the third component part has a composition such that it acts as a donor of constituents to the second component part the migration of which into the second component part reduces the migration of constituents of the first component part into the second component part.
The first component part may be silicon, and the third component part may be polysilicon. The second compartment part may be pure aluminium.
In one embodiment of the invention, the first component part defines an upper surface a portion of which defines the said surface of the first component part, a layer of insulating material is formed on the upper surface, a through hole is formed in the layer of insulating material over the said portion of the first component part, a layer of the third component part is formed on the layer of insulating material around the through hole, and the second component part is formed as a layer extending over the second component part and into the through hole.